Vehicle fuel systems are known to include a tank for holding fuel and a fuel fill pipe that functions as an inlet for supplying fuel to the tank from a nozzle at a refueling station. Vehicle fuel systems are known to include primary and secondary shutoffs to close the system.
The fuel fill pipe has an opening that can be exposed during refueling to receive the nozzle. Both capless and capped fuel fill pipes are known. An exposed end portion of the fuel fill pipe is of sufficient size to receive a discharge tube of a refueling nozzle at a fuel pumping system. It is known to have the nozzle fit relatively loosely in the fill pipe so that it can be inserted and removed easily, without undo physical interference. Accordingly, the fuel fill pipe is of greater diameter than the refueling nozzle, and a space exists between the nozzle and the fill pipe when the nozzle is position in the fill pipe.
Disadvantages experienced with some fuel systems during a refueling operation result from the relatively free airflow that can occur through the fill pipe via the space between the fuel fill pipe and the refueling nozzle outlet tube. The relatively brisk flow of fuel through the fuel fill pipe can entrain air therewith. The entrained air is readily replaced by air entering the fuel fill pip around the nozzle outlet tube, allowing the entrained air to be carried into the fuel tank. As the fuel tank fills with fuel, air displaced in the tank by the increasing volume of fuel is expelled from the tank. The expelled air carries hydrocarbons with it, whether the air was in the tank prior to when refueling commenced, or was carried into the tank by entrainment with the fuel stream entering the tank.
It is known to provide a vapor outlet system from the fuel tank, including a carbon canister to remove hydrocarbons from the air before the air is released into the atmosphere. However, since airflow is relatively unrestricted through the fill pipe and post the nozzle, escaping air and hydrocarbons from the tank can follow that path as well, avoiding the vapor outlet system and carbon canister, and being released into the atmosphere untreated.
The size of the carbon canister in the vapor outlet system is selected for the amount of hydrocarbons to be removed and for the volume of air to be processed through the canister. Accordingly, reducing air entrainment with the fuel during refueling, and thereby reducing hydrocarbon vapors expelled during refueling, reduces the hydrocarbon removal capacity required for the hydrocarbon canister. Decreasing the canister in both size and performance requirements can result in significant cost savings.